Signal output protection circuit of safety detection equipment

Abstract

The utility model discloses a signal output protection circuit of safety detection equipment. The signal output protection circuit comprises a high level module and a low level module which are connected in parallel between a signal input end and a signal output end, the high-level module comprises a first switch tube, a second switch tube, a first resistor, a second resistor and a first current limiting unit, and the first current limiting unit is connected with a base electrode and an emitting electrode of the second switch tube and a signal output side power supply positive end and used for limiting current from the high-level module to a signal output end; the low-level module comprises a third switch tube, a fourth switch tube, a third resistor, a fourth resistor and a second current limiting unit, and the second current limiting unit is connected with the base electrode, the emitting electrode and the ground end of the fourth switch tube and used for limiting current from the signal output end to the low-level module. According to the utility model, the problems of low fault tolerance and easy device damage of the output signal circuit of the existing safety detection equipment are solved, and the fault tolerance and the safety of the safety detection equipment in use are improved.

Description

Technical Field

[0001] This utility model relates to the field of detection technology, and in particular to a signal output protection circuit for a safety detection device. Background Technology

[0002] Safety detection equipment is a type of safety control device primarily used in mechanical or industrial equipment to protect operators from mechanical or electrical hazards that could cause injury. Common safety detection equipment includes safety light curtains, 3D cameras, and electromagnetic door locks. Taking a safety light curtain as an example, it typically consists of a series of photoelectric sensors (photodiodes) mounted around the machine. These sensors emit a light beam and stop or safely activate the equipment when they detect that the beam is blocked. Safety detection equipment achieves safety control by monitoring the position of personnel or objects within the equipment's working area, thereby preventing operators from approaching hazardous areas or causing unsafe events during equipment operation.

[0003] When an operator approaches a dangerous area, the safety detection equipment can output a danger signal to the host computer. At this time, the host computer will output a stop command to the equipment to shut it down. If the installer connects the signal output line incorrectly, for example, when the signal line outputs a high level and is grounded, the current will be too large. Similarly, when the output line outputs a low level and is mistakenly connected to a high voltage, the current will also be too large, which will burn out the transistor in the output circuit and cause a safety accident.

[0004] Chinese patent application CN202022854410.6 proposes a safety light curtain output protection circuit to provide overcurrent and overvoltage protection for the outputs of interfaces NPN-OUT and PNP-OUT. This solution is an open-drain output, which has weak driving capability for high-level outputs, and it uses an operational amplifier chip, resulting in relatively high cost.

[0005] In view of this, it is necessary to propose a new signal output protection circuit for security detection equipment to address the above-mentioned problems. Utility Model Content

[0006] The purpose of this utility model is to provide a signal output protection circuit for a safety testing device. By setting a current limiting unit, it solves the problem of low fault tolerance and easy damage to components in the output signal circuit of existing safety testing devices, thereby improving the fault tolerance and safety of the safety testing device.

[0007] This utility model provides the following solution:

[0008] This utility model proposes a signal output protection circuit for a safety detection device, including a high-level module and a low-level module connected in parallel between the signal input terminal and the signal output terminal;

[0009] The high-level module includes a first switching transistor, a second switching transistor, a first resistor, a second resistor, and a first current-limiting unit. The base of the first switching transistor is connected to the signal input terminal, the emitter is connected to ground, and the collector is connected to the positive terminal of the signal output power supply via the first resistor. The collector is also connected to the base of the second switching transistor via the second resistor. The collector of the second switching transistor is connected to the signal output terminal. The first current-limiting unit is connected to the base, emitter, and positive terminal of the signal output power supply of the second switching transistor, and is used to limit the current from the high-level module to the signal output terminal.

[0010] The low-level module includes a third switch, a fourth switch, a third resistor, a fourth resistor, and a second current-limiting unit. The base of the third switch is connected to the signal input terminal, the emitter is connected to ground, and the collector is connected to the positive terminal of the signal output power supply via the third resistor. The collector is also connected to the base of the fourth switch via the fourth resistor. The collector of the fourth switch is connected to the signal output terminal. The second current-limiting unit is connected to the base, emitter, and ground of the fourth switch to limit the current from the signal output terminal to the low-level module.

[0011] Optionally, the first, third, and fourth switching transistors are all NPN transistors, and the second switching transistor is a PNP transistor.

[0012] Optionally, the first current limiting unit includes a fifth switching transistor and a fifth resistor; the base of the fifth switching transistor is connected to the emitter of the second switching transistor, the collector is connected to the base of the second switching transistor, and the emitter is connected to the positive terminal of the power supply on the signal output side; the two ends of the fifth resistor are respectively connected to the positive terminal of the power supply on the signal output side and the emitter of the second switching transistor; the fifth switching transistor is a PNP transistor.

[0013] Optionally, the second current limiting unit includes a sixth switch and a sixth resistor; the base of the sixth switch is connected to the emitter of the fourth switch, the collector is connected to the base of the fourth switch, and the emitter is connected to ground; the two ends of the sixth resistor are respectively connected to the emitter of the fourth switch and ground; the sixth switch is an NPN transistor.

[0014] Optionally, the high-level module includes a first reverse polarity protection unit, which is disposed in the branch from the collector of the second switch to the signal output terminal; the low-level module includes a second reverse polarity protection unit, which is disposed in the branch from the collector of the fourth switch to the signal output terminal.

[0015] Optionally, the first reverse polarity protection unit is a first Schottky diode, with the anode of the first Schottky diode connected to the collector of the second switch and the cathode connected to the signal output terminal; the second reverse polarity protection unit is a second Schottky diode, with the cathode of the second Schottky diode connected to the collector of the fourth switch and the anode connected to the signal output terminal.

[0016] Optionally, the high-level module includes a first overcurrent protection unit, which is disposed in the branch from the collector of the second switch to the signal output terminal; the low-level module includes a second overcurrent protection unit, which is disposed in the branch from the collector of the fourth switch to the signal output terminal.

[0017] Optionally, the first overcurrent protection unit is a zero-ohm resistor, and the second overcurrent protection unit is a resistance wire.

[0018] Optionally, it also includes a feedback acquisition module connected to the signal output terminal. The feedback acquisition module includes an eighth resistor, a ninth resistor, and a Zener diode. The cathode of the Zener diode is connected to the signal output terminal via the eighth resistor, and the anode is connected to ground. The ninth resistor is connected in parallel across the Zener diode, and the cathode of the Zener diode serves as the signal feedback terminal.

[0019] Optionally, it also includes a tenth resistor, an eleventh resistor, and a twelfth resistor. The tenth resistor is connected between the base of the first switching transistor and the signal input terminal. The eleventh resistor is connected between the base of the third switching transistor and the signal input terminal. One end of the twelfth resistor is connected to the signal input terminal, and the other end is connected to the ground terminal or the positive terminal of the power supply on the signal input side.

[0020] This utility model has the following advantages compared with the prior art:

[0021] This invention discloses a signal output protection circuit for a safety detection device. The circuit employs a push-pull output design, offering fast switching speed and strong driving capability for both high and low-level signals. A first current-limiting unit restricts the conduction current of the second switching transistor, thereby limiting the output current supplied to the signal output terminal. This prevents damage to the switching transistor due to excessive current generated when the signal output terminal is mistakenly connected to a grounded terminal. Similarly, a second current-limiting unit restricts the conduction current of the fourth switching transistor, preventing damage to the switching transistor due to excessive current generated when the signal output terminal is mistakenly connected to a high level. This invention overcomes the problems of low fault tolerance and susceptibility to device damage in existing safety detection device output signal circuits, thus improving the fault tolerance and safety of the safety detection device.

[0022] Some embodiments of this utility model also prevent the circuit devices from being damaged by the reverse current input from the signal output terminal by setting a first reverse polarity protection unit and a second reverse polarity protection unit.

[0023] Some embodiments of this utility model also include a first overcurrent protection unit and a second overcurrent protection unit. When the current exceeds the limit, the first overcurrent protection unit and the second overcurrent protection unit will disconnect the circuit, thereby protecting other circuit components. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 These are schematic block diagrams of some embodiments of this utility model;

[0026] Figure 2 These are schematic block diagrams of some embodiments of this utility model;

[0027] Figure 3 These are schematic block diagrams of some embodiments of this utility model;

[0028] Figure 4 These are circuit schematic diagrams of some embodiments of this utility model;

[0029] Figure 5 These are circuit schematics of some embodiments of this utility model.

[0030] In the picture:

[0031] 100 - High-level module; 110 - First current limiting unit; 120 - First reverse polarity protection unit; 130 - First overcurrent protection unit; 200 - Low-level module; 210 - Second current limiting unit; 220 - Second reverse polarity protection unit; 230 - Second overcurrent protection unit. Detailed Implementation

[0032] The technical solution of this utility model will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0033] See Figures 1 to 5This utility model proposes a signal output protection circuit for a safety detection device, including a high-level module 100 and a low-level module 200 connected in parallel between the signal input terminal and the signal output terminal. The high-level module 100 includes a first switching transistor Q1, a second switching transistor Q2, a first resistor R1, a second resistor R2, and a first current-limiting unit 110. The base of the first switching transistor Q1 is connected to the signal input terminal, the emitter is connected to ground, and the collector is connected to the positive terminal of the signal output power supply (+24V) via the first resistor R1. The collector is also connected to the base of the second switching transistor Q2 via the second resistor R2. The collector of the second switching transistor Q2 is connected to the signal output terminal. The first current-limiting unit 110 is connected to the base, emitter, and positive terminal of the signal output power supply (+24V) of the second switching transistor Q2, and is used to limit the current from the high-level module 100 to the signal output terminal. The low-level module 200 includes a third switch Q3, a fourth switch Q4, a third resistor R3, a fourth resistor R4, and a second current-limiting unit 210. The base of the third switch Q3 is connected to the signal input terminal, the emitter is connected to ground, and the collector is connected to the positive terminal of the signal output power supply +24V via the third resistor R3. The collector is also connected to the base of the fourth switch Q4 via the fourth resistor R4. The collector of the fourth switch Q4 is connected to the signal output terminal. The second current-limiting unit 210 is connected to the base, emitter, and ground of the fourth switch Q4 and is used to limit the current from the signal output terminal to the low-level module 200.

[0034] In practice, the main control unit of the security detection equipment outputs a signal, which is then transmitted to other signal receiving devices via the signal output protection circuit. The main control unit and other signal receiving devices have different power supplies. As an example, the signal output by the main control unit can be a pulse signal with a defined period and width.

[0035] When the signal input terminal of the signal output protection circuit of the safety detection equipment receives a high-level signal, the first switch Q1 and the third switch Q3 of the high-level module 100 are both turned on, the second switch Q2 of the low-level module 200 is turned on, and the fourth switch Q4 is turned off. At this time, the +24V positive terminal of the signal output power supply can output current to the signal output terminal through the first current limiting unit 110 and the second switch Q2. The first current limiting unit 110 is used to limit the conduction current of the second switch Q2, thereby limiting the output current supplied to the signal output terminal, which can prevent the large current generated when the signal output terminal is accidentally grounded from burning out the switching devices.

[0036] When the signal input terminal of the signal output protection circuit of the safety detection equipment receives a low-level signal, the first switch Q1 and the third switch Q3 of the high-level module 100 are both turned off, the second switch Q2 of the low-level module 200 is turned off, and the fourth switch Q4 is turned on. At this time, there is no output current at the signal output terminal. If the external level connected to the signal output terminal is high, an external current will flow from the signal output terminal, through the fourth switch Q4, and through the second current limiting unit 210 to the ground terminal. The second current limiting unit 210 is used to limit the conduction current of the fourth switch Q4, which can prevent the large current generated when the signal output terminal is mistakenly connected to a high level from burning out the switch devices.

[0037] This utility model embodiment adopts a push-pull output form, which has a fast switching speed and strong driving capability for both high-level and low-level signal outputs. By setting the first current limiting unit 110 and the second current limiting unit 210, the problem of low fault tolerance and easy device damage in the output signal circuit of existing safety detection equipment is overcome, thereby improving the fault tolerance and safety of the safety detection equipment.

[0038] In some embodiments, see Figure 2 The first switch Q1, the third switch Q3 and the fourth switch Q4 are all NPN transistors, and the second switch Q2 is a PNP transistor.

[0039] In some embodiments, see Figure 2 The first current limiting unit 110 includes a fifth switch Q5 and a fifth resistor R5; the base of the fifth switch Q5 is connected to the emitter of the second switch Q2, the collector is connected to the base of the second switch Q2, and the emitter is connected to the positive terminal +24V of the signal output power supply; the two ends of the fifth resistor R5 are respectively connected to the positive terminal +24V of the signal output power supply and the emitter of the second switch Q2; the fifth switch Q5 is a PNP transistor.

[0040] In practical implementation, when the signal input terminal of the signal output protection circuit of the safety detection equipment receives a high-level signal, if the load current output from the signal output terminal increases, causing the voltage across the fifth resistor R5 to exceed 0.7V, the fifth switch Q5 will turn on, thereby pulling down the base voltage of the second switch Q2. This reduces the current output by the second switch Q2, thus keeping the voltage across the fifth resistor R5 constant at 0.7V. Since the voltage across the fifth resistor R5 is constant at 0.7V, the current through the fifth resistor R5 is also constant, thus ensuring a constant maximum current output from the signal output terminal. The specific current magnitude can be adjusted by changing the resistance value of the fifth resistor R5. By limiting the maximum current output from the signal output terminal, excessive current in the second switch Q2 can be prevented from burning out.

[0041] In some embodiments, see Figure 2The second current limiting unit 210 includes a sixth switch Q6 and a sixth resistor R6; the base of the sixth switch Q6 is connected to the emitter of the fourth switch Q4, the collector is connected to the base of the fourth switch Q4, and the emitter is connected to ground; the two ends of the sixth resistor R6 are connected to the emitter of the fourth switch Q4 and ground, respectively; the sixth switch Q6 is an NPN transistor.

[0042] In practical implementation, when the signal input terminal of the signal output protection circuit of the safety detection equipment receives a low-level signal, if the current flowing into the signal output terminal increases, causing the voltage across the sixth resistor R6 to exceed 0.7V, the sixth switch Q6 will turn on, thereby pulling down the base voltage of the fourth switch Q4. This reduces the output current of the fourth switch Q4, thus keeping the voltage across the sixth resistor R6 constant at 0.7V. Because the voltage across the sixth resistor R6 is constant at 0.7V, the current through the sixth resistor R6 is also constant, thus keeping the maximum current flowing through the fourth switch Q4 constant. The specific current magnitude can be adjusted by the resistance value of the sixth resistor R6. By limiting the maximum current, excessive conduction current of the fourth switch Q4 can be prevented from burning it out.

[0043] In some embodiments, see Figure 3 The high-level module 100 includes a first reverse polarity protection unit 120, which is disposed in the branch from the collector of the second switch Q2 to the signal output terminal; the low-level module 200 includes a second reverse polarity protection unit 220, which is disposed in the branch from the collector of the fourth switch Q4 to the signal output terminal.

[0044] In specific implementation, the first reverse polarity protection unit 120 and the second reverse polarity protection unit 220 are used to prevent the current input from the signal output terminal in reverse from damaging the circuit devices.

[0045] In some embodiments, see Figure 4 The first reverse polarity protection unit 120 is a first Schottky diode D1, the anode of which is connected to the collector of the second switch Q2 and the cathode is connected to the signal output terminal; the second reverse polarity protection unit 220 is a second Schottky diode D2, the cathode of which is connected to the collector of the fourth switch Q4 and the anode is connected to the signal output terminal.

[0046] In practical implementation, when the signal input terminal of the signal output protection circuit of the safety detection equipment receives a high-level signal, the +24V positive terminal of the signal output power supply can output current to the signal output terminal through the first current limiting unit 110, the second switch Q2, and the first Schottky diode D1. At this time, if there is a current input in reverse from the signal output terminal, it will be blocked by the first Schottky diode D1. When the signal input terminal of the signal output protection circuit of the safety detection equipment receives a low-level signal, if there is a current input in reverse from the signal output terminal, it will flow to the ground terminal through the second Schottky diode D2 and the fourth switch Q4.

[0047] In other embodiments, the first reverse polarity protection unit 120 and the second reverse polarity protection unit 220 may also be configured as ordinary diodes.

[0048] In some embodiments, see Figure 3 The high-level module 100 includes a first overcurrent protection unit 130, which is disposed in the branch from the collector of the second switch Q2 to the signal output terminal; the low-level module 200 includes a second overcurrent protection unit 230, which is disposed in the branch from the collector of the fourth switch Q4 to the signal output terminal.

[0049] In practical implementation, during the control dead zone, the second switch Q2 and the fourth switch Q4 may be turned on simultaneously, resulting in excessive current. The first overcurrent protection unit 130 and the second overcurrent protection unit 230 will disconnect the circuit when the current exceeds the limit, thereby protecting other circuit components.

[0050] In some embodiments, see Figure 4 The first overcurrent protection unit 130 is a zero-ohm resistor R7, and the second overcurrent protection unit 230 is a resistance wire F2.

[0051] When the signal input terminal of the signal output protection circuit of the safety detection equipment receives a high-level signal, a load current will flow through the first overcurrent protection unit 130. The first overcurrent protection unit 130 uses a zero-ohm resistor to avoid residual voltage drop and reduce power loss. The zero-ohm resistor will melt and blow when the current exceeds the limit to protect other components of the circuit.

[0052] In other embodiments, both the first overcurrent protection unit 130 and the second overcurrent protection unit 230 are resistance wires.

[0053] In some embodiments, see Figure 3 , Figure 4The signal output protection circuit of the safety detection equipment also includes a feedback acquisition module 300 connected to the signal output terminal OSSD. The feedback acquisition module 300 includes an eighth resistor R8, a ninth resistor R9 and a Zener diode D3. The cathode of the Zener diode D3 is connected to the signal output terminal through the eighth resistor R8, and the anode is connected to the ground terminal. The ninth resistor R9 is connected in parallel across the Zener diode D3. The cathode of the Zener diode D3 serves as the signal feedback terminal FK_OSSD.

[0054] In practical implementation, when the signal output terminal OSSD outputs current or receives incoming current, the signal feedback terminal FK_OSSD can output a feedback signal of a set level to the main control device of the safety detection equipment. The level of the feedback signal can be set by the Zener diode D3.

[0055] In some embodiments, see Figure 4 , Figure 5 It also includes a tenth resistor R10, an eleventh resistor R11, and a twelfth resistor R12. The tenth resistor R10 is connected between the base of the first switching transistor Q1 and the signal input terminal SC. The eleventh resistor R11 is connected between the base of the third switching transistor Q3 and the signal input terminal SC. One end of the twelfth resistor R12 is connected to the signal input terminal, and the other end is connected to ground (e.g., ...). Figure 4 (as shown) or the positive terminal of the power supply on the signal input side, MCU_VCC (e.g.) Figure 5 (As shown).

[0056] In practical implementation, the tenth resistor R10 is used to limit the base current of the first switching transistor Q1, and the eleventh resistor R11 is used to limit the base current of the third switching transistor Q3. The twelfth resistor R12 is used to set the initial input level of the circuit at the moment the device is powered on, and can be connected to ground (e.g., ...). Figure 4 (As shown) Set to low level, or connect to the positive terminal of the power supply MCU_VCC on the signal input side (e.g.) Figure 5 (As shown) is set to high level.

[0057] In some implementations, the security detection equipment product can also be equipped with two sets of signal output protection circuits for the security detection equipment, with the twelfth resistor R1 of one set connected to ground (e.g., Figure 4 As shown), the twelfth resistor R1 of the other group is connected to the positive terminal of the power supply MCU_VCC on the signal input side (as shown). Figure 5 (as shown), to be compatible with different initial signal states.

[0058] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0059] It should be noted that certain terms are used in this specification and claims to refer to specific elements. Those skilled in the art will understand that different manufacturers or producers may use different terms to refer to the same element. This specification and claims do not distinguish elements based on differences in terminology, but rather on differences in function.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features but not others included in other embodiments, combinations of features from different embodiments are intended to be within the scope of this invention and form different embodiments. For example, any one of the embodiments claimed in the claims can be used in any combination of embodiments of this invention.

[0062] Those skilled in the art will understand that modules in the device of the embodiments can be adaptively changed and placed in one or more devices different from that embodiment. Modules, units, or components in the embodiments can be combined into a single module, unit, or component, and further, they can be divided into multiple sub-modules, sub-units, or sub-components. Except where at least some of such features and / or processes or units are mutually exclusive, any combination can be used to combine all features disclosed in this specification (including the corresponding claims, abstract, and drawings) and all processes or units of any method or device so disclosed. Unless expressly stated otherwise, each feature disclosed in this specification (including the corresponding claims, abstract, and drawings) may be replaced by an alternative feature that serves the same, equivalent, or similar purpose.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model.

Claims

1. A signal output protection circuit for a safety detection device, characterized in that, Includes a high-level module (100) and a low-level module (200) connected in parallel between the signal input terminal and the signal output terminal; The high-level module (100) includes a first switch (Q1), a second switch (Q2), a first resistor (R1), a second resistor (R2), and a first current limiting unit (110). The base of the first switch (Q1) is connected to the signal input terminal, the emitter is connected to the ground terminal, and the collector is connected to the positive terminal (+24V) of the signal output power supply via the first resistor (R1). The collector is also connected to the base of the second switch (Q2) via the second resistor (R2). The collector of the second switch (Q2) is connected to the signal output terminal. The first current limiting unit (110) is connected to the base, emitter, and positive terminal (+24V) of the signal output power supply of the second switch (Q2) to limit the current from the high-level module (100) to the signal output terminal. The low-level module (200) includes a third switch (Q3), a fourth switch (Q4), a third resistor (R3), a fourth resistor (R4), and a second current-limiting unit (210). The base of the third switch (Q3) is connected to the signal input terminal, the emitter is connected to the ground terminal, and the collector is connected to the positive terminal (+24V) of the signal output power supply via the third resistor (R3). The collector is also connected to the base of the fourth switch (Q4) via the fourth resistor (R4). The collector of the fourth switch (Q4) is connected to the signal output terminal. The second current-limiting unit (210) is connected to the base, emitter, and ground terminal of the fourth switch (Q4) to limit the current from the signal output terminal to the low-level module (200).

2. The signal output protection circuit of a security detection device according to claim 1, characterized in that, The first switch (Q1), the third switch (Q3) and the fourth switch (Q4) are all NPN transistors, and the second switch (Q2) is a PNP transistor.

3. The signal output protection circuit of a security detection device according to claim 2, characterized in that, The first current limiting unit (110) includes a fifth switch (Q5) and a fifth resistor (R5); the base of the fifth switch (Q5) is connected to the emitter of the second switch (Q2), the collector is connected to the base of the second switch (Q2), and the emitter is connected to the positive terminal (+24V) of the power supply on the signal output side; the two ends of the fifth resistor (R5) are respectively connected to the positive terminal (+24V) of the power supply on the signal output side and the emitter of the second switch (Q2); the fifth switch (Q5) is a PNP transistor.

4. The signal output protection circuit of a security detection device according to claim 1, characterized in that, The second current limiting unit (210) includes a sixth switch (Q6) and a sixth resistor (R6); the base of the sixth switch (Q6) is connected to the emitter of the fourth switch (Q4), the collector is connected to the base of the fourth switch (Q4), and the emitter is connected to ground; the two ends of the sixth resistor (R6) are respectively connected to the emitter of the fourth switch (Q4) and ground; the sixth switch (Q6) is an NPN transistor.

5. The signal output protection circuit of a security detection device according to claim 1, characterized in that, The high-level module (100) includes a first reverse polarity protection unit (120), which is disposed in the branch from the collector of the second switch (Q2) to the signal output terminal; The low-level module (200) includes a second reverse polarity protection unit (220), which is disposed in the branch from the collector of the fourth switch (Q4) to the signal output terminal.

6. The signal output protection circuit of a security detection device according to claim 5, characterized in that, The first reverse polarity protection unit (120) is a first Schottky diode (D1), the anode of the first Schottky diode (D1) is connected to the collector of the second switch (Q2), and the cathode is connected to the signal output terminal; the second reverse polarity protection unit (220) is a second Schottky diode (D2), the cathode of the second Schottky diode (D2) is connected to the collector of the fourth switch (Q4), and the anode is connected to the signal output terminal.

7. The signal output protection circuit of a security detection device according to claim 1, characterized in that, The high-level module (100) includes a first overcurrent protection unit (130), which is disposed in the branch from the collector of the second switch (Q2) to the signal output terminal; the low-level module (200) includes a second overcurrent protection unit (230), which is disposed in the branch from the collector of the fourth switch (Q4) to the signal output terminal.

8. The signal output protection circuit of a security detection device according to claim 7, characterized in that, The first overcurrent protection unit (130) is a zero-ohm resistor (R7), and the second overcurrent protection unit (230) is a resistance wire (F2).

9. The signal output protection circuit of a security detection device according to claim 1, characterized in that, It also includes a feedback acquisition module (300) connected to the signal output terminal. The feedback acquisition module (300) includes an eighth resistor (R8), a ninth resistor (R9), and a Zener diode (D3). The cathode of the Zener diode (D3) is connected to the signal output terminal through the eighth resistor (R8), and the anode is connected to the ground terminal. The ninth resistor (R9) is connected in parallel across the Zener diode (D3), and the cathode of the Zener diode (D3) serves as the signal feedback terminal.

10. The signal output protection circuit of a security detection device according to claim 1, characterized in that, It also includes a tenth resistor (R10), an eleventh resistor (R11), and a twelfth resistor (R12). The tenth resistor (R10) is connected between the base of the first switching transistor (Q1) and the signal input terminal. The eleventh resistor (R11) is connected between the base of the third switching transistor (Q3) and the signal input terminal. One end of the twelfth resistor (R12) is connected to the signal input terminal, and the other end is connected to the ground terminal or the positive terminal of the power supply on the signal input side (MCU_VCC).

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